Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, and hard disk. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Data density is an important measured write head performance. Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. Data on magnetic media is often stored in a line or track. Magnetic media often have multiple tracks. In the case of the disk, the tracks are nested annular rings. More bits per ring and more rings per disk increases data density. Data density, therefore, is determined not only by the bit length, but also by the width of the bit which determines the track width. To decrease bit size, head size is decreased by fabricating thin film read and write heads. Thin film heads commonly employ separate write and read heads, which may be formed into a merged head structure.
Thin film write heads typically are formed by depositing and etching layers of magnetic, dielectric, and electrically conductive materials to provide the structures of the head. A typical write head has upper and lower pole structures having opposing pole tip portions separated by a write gap layer. A conductor winding, typically having an inorganic insulation stack such as cured photoresist, is formed on the conductors which surround a back gap.
In operation, the conductor winding generates magnetic flux through the pole structures and across the write gap at the pole tips. The write heads typically do not contact the magnetic media, but instead are separated from the magnetic media by a layer of air or air bearing. Magnetic flux generated across the write gap acts across the air bearing to change the magnetic moment of an area on the magnetic media.
As data bits are placed closer together to improve data density, a higher coercivity media is required to prevent bits from inadvertently being changed by adjacent bits, or by stray magnetic flux. As a result, a larger magnetic field across the write gap is required to set the bits. To produce this larger magnetic field, ever smaller structures must provide higher magnetic flux densities. Often, the structures of the write head are formed of high moment materials to provide the required flux densities.
High moment materials, though, are more sensitive to process techniques and write head architecture. Some high moment materials, for example, are more readily subject to corrosion if exposed to air. In addition, the magnetic properties of high moment materials can degrade if deposited over sloped surfaces. Further, the present inventors also have observed that materials sputtered on the sloped areas of stack insulation can deposit with a porous or rough surface that can degrade the magnetic properties of any materials plated thereon. Additionally, the rough surface can diffract light during the photolithographic exposure process, reducing mask sharpness and impacting pole tip definition.
In addition to requiring high moment materials, production of larger magnetic fields also requires greater magnetomotive force. As such, optimum performance of the conductor winding also is important. One impediment to optimum performance observed by the present inventors is that conductors can corrode or oxidize within the stack insulation, thus increasing operating temperature and conductor resistance. This can occur during the insulation stack curing process and cause a shell of oxidation to form on the surface of the conductor.
Another problem associated with conventional windings identified by the present inventors is that pin holes in the stack insulation can cause shorting to the upper pole structure. This is more likely to occur as stack insulation height is reduced to improve write head performance. Also, etching or milling to define the upper pole structure from high Bsat, or other sputtered material, can result in milling through outlying portions of the stack insulation and into the conductor winding, thus reducing conductor winding performance.
A further drawback with conventional write heads noted by the present inventors is that thermal expansion of cured photoresist stack insulation can degrade write head performance. It can cause a magneto-strictive effect in the pole material which can cause a rotation of the easy axis, reducing the high frequency response of the write head. Further, thermal expansion can ultimately lead to delamination of stack insulation and the upper pole structure.
Embodiments in accordance with the thin film write head of the present invention have a lower pole structure, an upper pole structure, and a multilayer write gap extending from an air bearing surface between the upper and lower pole structures. In preferred embodiments, the write gap comprises at least two of: (a) a first layer covering a lower pole tip portion of the lower pole structure, (b) a second layer covering turns of a conductor winding, or (c) a third layer covering a winding insulation stack. In more preferred embodiments, the write gap is formed of the first, the second, and the third write gap layers.
An advantage of a write head with a multilayer write gap is that it allows better control of write gap thickness. As such, loss of write gap thickness can be compensated for by deposition of the second write gap layer, or by deposition of the third write gap layer. Furthermore, the thickness of a subsequently deposited write gap layer/layers may be selected during processing to compensate for unintended loss of first or second write gap layers occurring during write head fabrication. As such write head performance and yield may be better controlled.
In addition, embodiments having the first write gap layer can inhibit oxidation of the planarized lower pole tip during conductor fabrication, which is of particular importance when the lower pole tip is formed of high moment materials more susceptible to corrosion.
Embodiments having the second write gap layer can inhibit corrosion or oxidation of the conductor turns that can form during the curing process used to form the stack insulation. The second write gap layer also may serve as a corrosion protection layer for the lower pole tip during the stack insulation curing process, particularly in embodiments not employing the first write gap layer. Also, the second write gap layer can reduce the roughness of the surface of the coil turns, which may reduce the roughness of the top surface of the stack insulation resulting in improved material properties of the upper pole structure.
Embodiments having the third write gap layer can improve the properties of overlying high moment materials. Moreover, the third write gap layer can reduce magneto-strictive effects and delamination of the write head structures. Also, the third write gap may provide added protection of outlying stack insulation and conductor turns during ion milling processes.
Further, embodiments having the second and/or third write gap layer allow stack insulation height to be reduced by serving as additional protection against shorting of the conductor turns. As such, shorting due to pin holes or other stack insulation non-uniformity may be inhibited in reduced stack height writers.